Document U.S. Pat. No. 8,303,167B2 discloses a mechanism for a timepiece, comprising a regulator mechanism having a periodical movement, two rotary escapement wheels, a blocking mechanism cooperating with the escapement wheels, said distributor mechanism being controlled by the regulator mechanism to regularly and alternatively hold and release the escapement wheels so that said escapement wheels rotate step by step, and an bistable elastic member configured to be cyclically deformed in a predetermined way to store energy, and to release this energy to the regulator mechanism by elastic return.
This mechanism is very complex, hence costly, and includes a large number of parts moving with frictional losses, which limits the energetic efficiency of the system.